Juvenile polymyositis associated with anti-OJ (anti-isoleucyl-tRNA synthetase) autoantibody in a 13-year-old girl.

A 13-year-old girl was admitted for persistent thigh pain and remittent fever and was diagnosed as having juvenile polymyositis. Although the initial treatment with 2 cycles of methylprednisolone pulse therapy failed to achieve full remission, the second-line treatment with intravenous cyclophosphamide pulse therapy was effective. Anti-OJ antibody, which is one of anti-aminoacyl-tRNA synthetase (ARS) antibodies and is rare in adult polymyositis, was detected. Assessment of anti-ARS autoantibodies may facilitate diagnosis and management of juvenile polymyositis.